Software must be designed in detail before development starts, so that a clear plan can be out-layed. The truth) The more complex a design, the more like software the design itself is. By perfecting a design, then writing the software to that design, you're effectively writing the work twice. Instead, by doing just some simple design sketches and data modelling rather than a book-like design, a good development team can create a shell for the software and efficiently refine it towards the finished product.

This process of refinement creates natural prototypes, allows easy adaptation when issues that would be unforseen by a design arise (or brought up as fresh concerns by a client), and the total process takes significantly less time. To pull this off requires a close team, skill, and experience, but it is by far the best option for the majority of situations.